SpaceX successfully launched the X-37B, an autonomous space drone for the Air Force that's slated for a 270-day mission. The Air Force has not disclosed what the drone will be doing. (SpaceX)

This post has been updated.

In the Pentagon's vast arsenal there is little quite like it: a super-secret space drone that looks like a miniature version of the space shuttle, but orbits the Earth for months, even years, at a time. Doing what? The Air Force won't say.

On the tarmac, the X-37B, as it is called, looks tiny, standing not much taller than a person. Its wingspan measures less than 15 feet, and it weighs in at just 11,000 pounds. But over the course of six flights, it has proved to be a rugged little robotic spacecraft, spending a total of nearly six years probing the hard environment of the high frontier.

On Thursday, after a successful morning launch at the Kennedy Space Center in Florida, the X-37B headed yet again to the vital real estate known as low Earth orbit, home to the International Space Station and all sorts of military and commercial satellites. The mission is slated to last 270 days, but the Air Force warned in a statement that “the actual duration depends on test objectives, on-orbit vehicle performance and conditions at the landing facility.”

In other words, there’s no telling how long the thing will be up there.

On a fact sheet, the Air Force says that, “the primary objectives of the X-37B are twofold: reusable spacecraft technologies for America's future in space and operating experiments which can be returned to, and examined, on Earth.”

On this flight, the Air Force will say only that the mission is to carry small satellites, “demonstrate greater opportunities for rapid space access and on-orbit testing of emerging space technologies.” The service also said it would test experimental electronics in a weightless environment.

But at a time when space is becoming a contested environment, having an orbiting spaceplane with the potential to keep a lookout on weather or the enemy or satellites, all while testing new technologies, could be highly beneficial.

The mission is also significant because it marked the first time SpaceX has been chosen to launch for the Air Force — a coup for the California firm started in 2002 by tech entrepreneur Elon Musk.

The launch took place as the Pentagon sounds the alarm about the importance of defending the ultimate high ground should war break out in space. More recently, the House has even pushed for the creation of a separate "Space Corps" within the Air Force designed to focus exclusively on the beyond.

The provision, included in the House's version of the defense spending bill, comes amid concerns that Russia and China are quickly eroding the advantage that the United States has held in orbit for years.

“Space has become so critical to the way we fight and win wars, it can no longer be subordinate,” Rep. Mike D. Rogers, a Republican from Alabama who serves on the House Armed Services Committee, said at an event this week at the Center for Strategic and International Studies. The Space Corps would focus on “space domination,” he said, with a dedicated leadership and resources that would allow it to move more nimbly than the Pentagon bureaucracy.

“The Air Force is about as fast a herd of turtles as far as space is concerned,” he said. “What Russia and China are doing is startling.”

While most agree that space is an increasingly important military domain, support in the Senate for a new separate military branch is far from assured. And many in the upper reaches of the Pentagon also oppose it.

The X-37B was launched on top of a SpaceX Falcon 9 rocket. SpaceX also successfully landed the first stage on a landing pad on the Cape--a bit of rocket artistry that Musk and others have said could help dramatically lower the cost of space travel. By now the feat is becoming routine for the company, which plans to reuse its boosters instead of throwing them away after each launch, as had been the traditional practice.

Musk’s space company had been fighting to enter the national security launch market for years.

For nearly a decade, the United Launch Alliance, the joint venture between Lockheed Martin and Boeing, had a monopoly on Pentagon launches. SpaceX filed suit against the Air Force for the right to compete. In 2015, the parties settled and SpaceX was ultimately allowed to compete against ULA, opening up a potentially lucrative source of revenue. Since then, SpaceX has won two of three contested launch contracts.

While the launch of the X-37B was not competed — ULA President Tory Bruno has said that his company was not given the option to bid — it marks SpaceX’s first military mission after years of launching payloads for NASA and commercial satellites. All four of the X-37B's previous launches were aboard ULA's Atlas V rocket.

The Pentagon said it was grateful to have two companies with the ability to launch, introducing competition, and lower prices.

“The benefit we’re seeing now is competition,” Air Force Secretary Heather Wilson said during a June Senate hearing. “There are some very exciting things happening in commercial space that bring the opportunity for assured access to space at a very competitive price.”